The detrimental effects of long term exposure to low concentrations of lead are not well understood. A recent observation from this laboratory indicates that increased cardiac risk may occur as a latent sequela to lead exposure during early post-natal development in rats. The proposed study is designed to further examine the nature of this phenomenon by determining the relationship of exposure time and lead concentration to effect, and the specificity of the cardiac response. Suckling rats will receive lead via mother's milk for a part of the whole of the nursing period (21 da.). Concentrations of lead in blood and heart will be determined by atomic absorption spectrophotometry after various lengths of treatment. Animals will be placed on a normal diet for 3 months prior to cardiac testing. The effect of norepinephrine and other drugs on cardiac rhythm will be examined in vivo and in the isolated perfused heart. Biochemical analyses of autonomic neurotransmitter production and metabolism in the hearts of lead-exposed animals will be performed to evaluate the integrity of the cardiac autonomic system. Data from this study should allow us to define the nature of lead cardiotoxicity, and predict the risks involved in low level lead exposure.